Count frequencies of all elements in array in O ( 1 ) extra space and O ( n ) time | C # program to print frequencies of all array elements in O ( n ) extra space and O ( n ) time ; Function to find counts of all elements present in arr [ 0. . n - 1 ] . The array elements must be range from 1 to n ; Hashmap ; Traverse all array elements ; Update the frequency of array [ i ] ; Increase the index ; Driver code
using System ; class GFG { public static void findCounts ( int [ ] arr , int n ) { int [ ] hash = new int [ n ] ; int i = 0 ; while ( i < n ) { hash [ arr [ i ] - 1 ] ++ ; i ++ ; } Console . WriteLine ( " STRNEWLINE Below ▁ are ▁ counts ▁ " + " of ▁ all ▁ elements " ) ; for ( i = 0 ; i < n ; i ++ ) { Console . WriteLine ( ( i + 1 ) + " ▁ - > ▁ " + hash [ i ] ) ; } } static public void Main ( ) { int [ ] arr = new int [ ] { 2 , 3 , 3 , 2 , 5 } ; findCounts ( arr , arr . Length ) ; int [ ] arr1 = new int [ ] { 1 } ; findCounts ( arr1 , arr1 . Length ) ; int [ ] arr3 = new int [ ] { 4 , 4 , 4 , 4 } ; findCounts ( arr3 , arr3 . Length ) ; int [ ] arr2 = new int [ ] { 1 , 3 , 5 , 7 , 9 , 1 , 3 , 5 , 7 , 9 , 1 } ; findCounts ( arr2 , arr2 . Length ) ; int [ ] arr4 = new int [ ] { 3 , 3 , 3 , 3 , 3 , 3 , 3 , 3 , 3 , 3 , 3 } ; findCounts ( arr4 , arr4 . Length ) ; int [ ] arr5 = new int [ ] { 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 } ; findCounts ( arr5 , arr5 . Length ) ; int [ ] arr6 = new int [ ] { 11 , 10 , 9 , 8 , 7 , 6 , 5 , 4 , 3 , 2 , 1 } ; findCounts ( arr6 , arr6 . Length ) ; } }